[mach-o] add support for old x86 __eh_frame sections

Over time the symbols and relocations have changed for dwarf unwind info
in the __eh_frame section.  Add test cases for older and new style.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@213585 91177308-0d34-0410-b5e6-96231b3b80d8